1. Field of the Invention
This invention relates to a novel electrolytic process for preparing alkyltin halide compositions particularly dialkyltin dihalides and trialkyltin halides. In one embodiment of the invention, the corresponding solid oxides are produced which are easily separated from the liquid portion of the reaction mixture.
2. Description of the Prior Art
One class of commercially important alkyltin compositions comprises tetravalent alkyltin compositions wherein the unsatisfied valences are satisfied by halogen atoms. Such compositions find wide and well-known utility as, for instance, catalysts for esterifications and as intermediates through which other tetravalent alkyltin compositions are prepared for specialized uses.
Dialkyltin dihalides, such as dibutyltin dichloride and dioctyltin dichloride are becoming increasingly important as intermediates for preparing such commercial products as dibutyltin diacetate, dibutyltin dilaurate, dioctyltin dilaurate and the like and as independent articles of commerce.
Existing methods for preparing the dialkyltin dihalides involve costly and time consuming operations. One such process involves first preparing the tetraalkyltins, then degrading them to the dialkyltin compositions, for example, by reaction with halogen. Another process involves reacting preformed tetraalkyltin with a stannic halide to form redistribution mixtures of the various possible tetravalent alkyltin halides. Still another process involves direct reaction of tin with alkyl halides. This process, even with the use of catalysts, requires rather high temperatures and pressures and extended periods of time to effect the desired results.
U.S. Pat. No. 3,197,382 discloses the preparation of tetraalkyltins (among other organo metal compositions) by the electrolytic reduction of alkyl esters (including alkyl halides) at a tin cathode (or other sacrificial metal cathode according to the organo metal to be prepared). Cleaving alkyl groups from the tetraalkylated product by breaking the alkyltin bond in order to obtain alkyltins having less than four alkyls per tin atom would constitute a waste of the electricity already utilized and required to form those alkyltin bonds in the electrolytic process.
Russian Patent No. 184853 discloses preparation of alkyltin halides by electrolyzing a mixture of alkyl halides and tin salts at a magnesium cathode, e.g., electrolyzing butyl bromide and tin chloride in butyl acetate in contact with a magnesium cathode and a graphite anode while gradually adding bromine during the electrolysis yielded a mixture of dibutyltin dibromide and tributyltin bromide.
A process has now been discovered for preparing alkyltin compositions containing less than four alkyl groups per tin atom, which process, among other things, (1) avoids the stringent conditions of temperature and pressure required to produce alkyltin halides by direct reaction of tin with alkyl halides; (2) avoids the necessity of proceeding via cleavage of alkyl group from tetraalkyltins to the desired compositions.